“The bottom line is that the protective effects of vitamin D supplementation are strongest in those who have the lowest vitamin D levels, and when supplementation is given daily or weekly rather than in more widely-spaced doses,” lead researcher, Adrian Martineau, said in a statement.

Boosting immunity

The research team at Queen Mary University of London (QMUL) concluded that vitamin D protects the human body against respiratory infections, including bronchitis and pneumonia, by boosting levels of antibiotic-like peptides in the lungs.

This assumption fits with an observation that colds and flu are more common in fall and winter, when vitamin D levels are the lowest.

It may also explain why vitamin D seems to protect against asthma attacks, they said.

Louis Levy, head of Nutrition Science at Public Health England, however, said the study requires scientific confirmation.

“This study does not provide sufficient evidence to support recommending vitamin D for reducing the risk of respiratory tract infections,” he was quoted as saying by the London Science Media Center.

Meanwhile, the UK National Institute for Health Research said the findings were “worthy of serious further debate.”

Ultimately, the research team from QMUL wanted vitamin D to be added to food like milk.

Vitamin D is found in foods such as fish, egg yolks, meat and cereals, in addition to fruits and vegetables.